Method for recycling precious metal from used printed circuit boards

ABSTRACT

A method is disclosed for recycling precious metal from used printed circuit boards. The used printed circuit boards are roasted with plasma at 800 degrees Celsius for less than 10 minutes, thus producing exhaust and residue that contains the precious metal. The exhaust is treated with an exhaust-treatment system before it is released to the atmosphere. The residue is ground and turned into scraps of a diameter smaller than 2 mm. The scraps are subjected to magnetic separation, thus separating ferromagnetic scraps from non-ferromagnetic scraps. The ferromagnetic scraps are refined. The non-ferromagnetic scraps are screened, thus separating tiny non-ferromagnetic scraps from big non-ferromagnetic scraps. The tiny non-ferromagnetic scraps contain silver and gold. The big non-ferromagnetic scraps contain copper.

FIELD OF THE INVENTION

The present invention relates to printed circuit boards and, more particularly, to a method for recycling precious metal from used printed circuit boards.

DESCRIPTION OF THE RELATED ARTS

Printed circuit boards contain precious metal such as gold, silver and copper. It is not only environmentally hazardous but also economically wasteful to dispose of used printed circuit boards without recycling the precious metal.

As disclosed in Taiwanese Patent Publication Nos. 247281 and 363904, used printed circuit boards are smashed before precious metal such as the gold, silver and copper is recycled. It, however, requires a lot of energy to smash the used printed circuit boards since they are composed of mainly elastic resin. Moreover, a lot of dust and noise are made. In addition to these drawbacks, machines for smashing the used printed circuit boards wear away substantially.

As disclosed in Taiwanese Patent Publication 1268184, used printed circuit boards are incinerated before precious metal such as the gold, silver and copper is recycled. It, however, requires a lot of energy and takes a lot of time to incinerate the used printed circuit boards.

The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide a method for recycling precious metal from used printed circuit boards.

To achieve the foregoing objective of the present invention, in a method, used printed circuit boards are roasted with plasma at 800 degrees Celsius for less than 10 minutes, thus producing exhaust and residue that contains the precious metal. The exhaust is treated with an exhaust-treatment system before it is released to the atmosphere. The residue is ground and turned into scraps of a diameter smaller than 2 mm. The scraps are subjected to magnetic separation, thus separating ferromagnetic scraps from non-ferromagnetic scraps. The ferromagnetic scraps are refined. The non-ferromagnetic scraps are screened, thus separating tiny non-ferromagnetic scraps from big non-ferromagnetic scraps. The tiny non-ferromagnetic scraps contain silver and gold. The big non-ferromagnetic scraps contain copper.

Other objectives, advantages and features of the present invention will become apparent from the following description referring to the attached drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described via detailed illustration of the preferred embodiment referring to the attached drawing.

FIG. 1 is a flowchart of a method for recycling precious metal from used printed circuit boards according to the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENT

Referring to FIG. 1, there is shown a method for recycling precious metal from used printed circuit boards according to the preferred embodiment of the present invention.

At 1, used printed circuit boards are collected.

At 2, the used printed circuit boards are roasted with plasma so that the resin in the used printed circuit boards is decomposed. The plasma-based roasting is conducted at a temperature of 800 degrees Celsius for a period of 10 minutes. Exhaust 21 is produced as a byproduct. The residue 22 left as the result of the plasma-based roasting contains the precious metal and glass fibers.

AT 3, the exhaust 21 produced because of the plasma-based roasting is treated with an exhaust-treatment system, and hereinafter released to the atmosphere.

At 4, the residue 22 is ground into scraps 41 of a diameter smaller than 2 mm.

At 5, the ground scraps 41 are subjected to magnetic separation so that ferromagnetic scraps 51 are separated from non-ferromagnetic scraps 52.

At 6, the ferromagnetic scraps 51 are refined in an iron refinery.

At 7, the non-ferromagnetic scraps 52 are sifted by a screen with meshes of 0.149 mm in diameter. Therefore, tiny non-ferromagnetic scraps 71 are separated from big non-ferromagnetic scraps 72. The tiny non-ferromagnetic scraps 71 that contain gold and silver are smaller than 0.149 mm in diameter. The big non-ferromagnetic scraps 72 that contain copper are larger than 0.149 mm in diameter.

At 8, the tiny non-ferromagnetic scraps 71 are processed in a precious metal refinery so that the gold and silver are recycled.

At 9, the big non-ferromagnetic scraps 72 are processed in a copper smelter so that the copper is recycled.

The method according to the present invention exhibits several advantages over the methods discussed in the RELATED PRIOR ART. The resin of the used printed circuit boards is roasted and decomposed with the plasma. Therefore, the first advantage is the relatively low energy needed to grind the residue 22.

Secondly, the wearing out of grinding machines is reduced.

Thirdly, it is relatively friendly to the atmosphere because the exhaust 21 is treated before it is released.

Fourthly, it is economically worthwhile for recycling the precious metal such as gold, silver, copper and iron.

Fifthly, it is relatively friendly to the environment because relatively little material is disposed of as waste.

Sixthly, it is safe.

The present invention has been described via the detailed illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims. 

1. A method for recycling precious metal from used printed circuit boards, the method comprising the steps of: roasting the used printed circuit boards with plasma at 800 degrees Celsius for less than 10 minutes, thus producing exhaust and residue that contains the precious metal; treating the exhaust with an exhaust-treatment system before releasing it to the atmosphere; grinding the residue and turning it into scraps of a diameter smaller than mm; subjecting the scraps to magnetic separation, thus separating ferromagnetic scraps from non-ferromagnetic scraps; refining the ferromagnetic scraps; screening the non-ferromagnetic scraps, thus separating tiny non-ferromagnetic scraps from big non-ferromagnetic scraps, wherein the tiny non-ferromagnetic scraps contain silver and gold, while the big non-ferromagnetic scraps contain copper.
 2. The method according to claim 1, wherein the tiny non-ferromagnetic scraps are smaller than 0.149 mm in diameter.
 3. The method according to claim 1, wherein the big non-ferromagnetic scraps 72 are larger than 0.149 mm in diameter. 